In many applications signals need to be transmitted between circuits operated at different electric potentials. The electric potential difference between the respective circuits can be up to several hundreds volts or even higher.
Commonly, level shifters have been used to transmit signals between circuits at different electric potentials. Level shifters include a switching element such as a MOS transistor, the breakdown voltage of which is above the electric potential difference between the circuits to generate a set pulse and a reset pulse. The pulses are generated by operating the switching element which causes a current pulse in the receiving circuit. The current pulse is detected, for example by detecting a voltage drop over a resistor in the receiving circuit.
The use of level shifters is limited to a frequency range of up to about 300 kHz or, if a silicon-on-insulator (SOI) substrate is used, of up to about 600 kHz due to inherent large dynamical parasitic capacitances.
Another option for signal transmission between circuits at different electric potentials is provided by coreless transformers which include coils arranged, for example, above each other and which are insulated from each other by an insulating material. Coreless transformers provide for a signal transmission in the MHz range.